The present invention relates to glass producing apparatus, and more particularly to improved means for supplying vaporized source material to an apparatus for forming blanks to be drawn into optical waveguides.
Certain glass making processes, particularly vapor deposition processes used to form optical waveguide blanks, utilize a flame to which a vaporous source material is added. In the flame the source material becomes a soot which is deposited upon a rod or tube in successive layers until a desired size is obtained. The rod may then be removed and the finished item is then heated and fused into a glassy member referred to as a blank. In another process the vaporous source material is directed into a heated tube. The material is deposited within the tube in successive layers to produce a fused blank. The blank is subsequently heated and drawn into an elongate, fine strand. Inasmuch as the structure of the drawn strand reflects the structure of the drawing blank, it is important that the physical characteristics of the blank be carefully controlled. This is particularly true in forming optical waveguides, since small inclusions and other imperfections can virtually destroy the utility of the guide. In addition the index of refraction of the material must be carefully controlled.
As is familiar to those skilled in the art, optical waveguides commonly exhibit a first, higher index of refraction near the core or center thereof; and a second, lower index of refraction at a point radially outward from the core. The gradient of the index of refraction may be varied continuously or discontinuously, and may exhibit a linear, parabolic, or other desired characteristic. Information concerning the construction and use of optical waveguides may be found in "Fiber Optics Principles and Applications" by N. S. Kapany, Academic Press, 1967; "Geometrical Optics of Parabolic Index-Gradient Cylindrical Lenses" by F. P. Kapron, Journal of the Optical Society of America, Vol. 60, No. 11, pages 1433-1436, November 1970 and "Cylindrical Dielectric Waveguide Mode" by E. Snitzer, Journal of the Optical Society of America, Vol. 51, No. 5, pages 491-498, May 1961.
In order to effect a change in the index of refraction of a blank being formed by the vapor deposition process, the chemical composition of the source materials which comprise the deposited soot may be varied. For example, a hydrolyzing and/or oxidizing burner may be supplied with a silicon-bearing vapor. The vapor mixture is hydrolyzed to form a glass soot which is subsequently fused to form a high quality glass. At the same time, one or more additional vapors can be supplied to the hydrolyzing burner, each vapor being constituted of a chemical termed a "dopant" whose presence affects the index of refraction of the glass being formed.
In order to form a blank having generally consistent properties, and to assure an even distribution of the glass-forming soot, it is necessary to supply a hydrolyzing burner with a substantially constant flow of vaporized source material entrained in a carrier gas. Accordingly, systems have been devised for controlling the carrier gas flow, and the rate at which source material is vaporized and entrained into the carrier gas. Due in part to the multiplicity of factors which determine the amount of vapor introduced into a hydrolyzing flame at any given time, fluctuations in the deposition rate of the various vapor deposition processes often occur. Accordingly, it will be appreciated that it would be highly desirable to provide a system for delivering vaporized source material to a hydrolyzing burner in a consistent, highly controllable fashion.
It is therefore a object of the present invention to provide improved apparatus for supplying vaporized source material to a vapor deposition means.
Another object of the present invention is to provide improved apparatus for controllably vaporizing liquid source material.
Yet another object of the invention is to provide apparatus which assures the entrainment of a precise amount of source material in a carrier gas.
Still another object is to provide a system for entraining liquid source material in a carrier gas with a higher precision than any heretofore known.